1. Field of the Invention
The invention relates to assembling a butterfly valve and a rotary shaft which passes through a duct and in which a slot is formed for receiving the butterfly valve. It is particularly although not exclusively suitable for use in the fitting of butterfly valves forming a restriction member in fuel supply devices for internal combustion engines.
The intake ducts of such engines generally comprise a butterfly valve controlled by the driver for metering the flow rate of an air/fuel mixture delivered to the engine. Many carburetors further comprise a second butterfly valve, forming a starting choke and which is placed in the air intake of the carburetor and whose purpose is to increase the fuel/air ratio of the mixture delivered to the engine during a cold start.
2. Prior Art
Sometimes, the butterfly valve is fastened by screws on a flat formed on the shaft. Much more often, the butterfly valve is placed in a slot formed through the shaft and it is held in position by screws passing through the shaft and the butterfly valve or by resilient projections of the valve (U.S. Pat. Nos. 2,105,343 and 1,841,695).
At first sight, the fitting of the butterfly valve seems a simple operation. In fact, it is difficult, particularly because the clearance between the butterfly valve and the walls of the slot must be very small (a few hundredths of a millimeter) to avoid air leaks through this gap. To fit the butterfly valve, the shaft must first of all be indexed so that the slot is parallel to the axis of the duct, then the butterfly valve must be inserted over the required height and finally the shaft-butterfly valve units is rotated while preventing the butterfly valve from sliding in the slot, as far as the closed position in which the fastening screws are inserted. Up to now, the butterfly valve has been inserted in the correct position and then held in position by hand while the shaft is rotated.